What does a pH measurement indicate in soil?

A pH measurement in soil primarily indicates the relative acidity or alkalinity of the soil. This is crucial for understanding soil chemistry because pH affects nutrient availability, microbial activity, and overall soil health. Each soil type has an optimal pH range that supports most plant growth; for example, most plants thrive in slightly acidic to neutral conditions (around pH 6 to 7). Measurements outside this range can limit nutrient absorption and affect plant health.

The other options, while related to soil characteristics, do not directly relate to what pH measures. Organic matter content, soil moisture level, and nutrient content involve different specific analyses and tests that do not provide insight into the soil's pH level directly.